Hi Tom, if no snapping is activated, then the mouse will track along the construction plane, shooting a ray out through the mouse point and intersecting it with the construction plane grid.

If you're looking at the grid at such an angle that a small distance of the mouse moves a very far distance along that grid it will have the kind of effect that you describe.

To avoid that, angle your view so you're looking somewhat more downward at the grid instead of having it positioned where it's going way off into the horizon.

Either that or you may need to set the construction plane to better accomodate the kind of thing you want to draw. Basically your mouse will track along that plane.

- Michael